1. Field of the Invention
This invention relates to pallets of the type used in gravity-flow rack systems, and in particular, it relates to a type of pallet that has a deck formed of hollow steel tubes and supporting members formed of sheet steel. The support members have roller contact areas and are welded to the deck tubes to produce a pallet structure of greater strength and rigidity than gravity-flow pallets known heretofore.
2. Prior Art
Gravity-flow rack systems are used for storage and transportation of goods within a warehouse or other storage area. The racks include parallel rail systems with rollers mounted on them and extending above the upper surface of the rails, and the pallets to be used in such systems having flanges, or wings, extending laterally outward so that they can rest on the rollers to move easily along the rails with only low rolling friction to be overcome. By constructing the racks so that they are inclined in the right direction, the force of gravity is sufficient to move the pallets, loaded or not, and it is unnecessary to supply additional motive power.
One of the advantages of the gravity-flow system is that it forces a certain order in the transfer of the stored material from an entrance location to an outlet location. The fact that the pallets move under the force of gravity causes those that were first entered at the upper end of the system to emerge first from the lower end of the system, i.e. the storage on the inclined racks is first-in-first-out. This is especially useful in the case of products that may be subject to deterioration with age, such as food products, but it is also useful in maintaining orderly inventory turnover of products that do not deteriorate.
Pallets made heretofore for use in gravity-flow rack systems have most commonly used wooden deck planks with sheet metal tracks along two opposite edges to rest on the uppermost surface of the rollers supported by the rails. One of the disadvantages of such pallets is that the wood is subject to deterioration in use and needs to be replaced relatively frequently. The sheet metal tracks can be pulled away from the deck planks relatively easily, or even destroyed, so that such pallets are likely to require substantial repair or replacement twice a year.
Pallets with wood comprising the main portion are shown in U.S. Pat. No. 3,026,817. The pallets in that patent have sheet metal edge portions attached along opposite edges to engage and be guided by rollers spaced along the track. While not all pallets that use wood as a main construction component have the type of multi-layer deck shown in U.S. Pat. No. 3,026,817, they are still likely to be relatively heavy, and typically about 75 pounds for a wooden pallet 48" long and 40" wide, which is one of the most popular sizes.
Several forms of plastic or plastic-coated pallets are described in U.S. Pat. Nos. 3,330,228; 3,707,929; and 3,760,741. In the latter two, the edges of the pallets that extend over track rollers are covered by sheet metal attached to the plastic to conform to the shape of the pallet structure and to rest directly on the rollers. Such plastic and plastic-coated pallets are subject to breakage when they are engaged by the tines of a fork lift truck or the like. Furthermore the plastic structure requires a mold, which tends to fix the size of the pallets and to prevent an easy change in production of pallets from one size to another. Plastic pallets, such as are shown in U.S. Pat. No. 3,330,228, that have no sheet metal components to rest on the rollers are likely to be subjected to a good deal of wear and tear in usage. Even those pallets that do have sheet metal rails, such as are shown in U.S. Pat. Nos. 3,707,929 and 3,760,741, run the risk of having the sheet metal rails separated from the plastic part of the pallets in the same way as pallets that have wooden decks.
In gravity-flow rack systems, it is desirable to be able to make the tracks relatively long so that a large number of pallets can be lined up, one behind the other. In addition, it is common to provide a tunnel structure that makes the pallets relatively inaccessible except at the entrance and outlet ends. However, a long track, and particularly a tunnel, makes it necessary that the pallets follow the rails precisely and not go askew. In the case of pallets made of wood with sheet metal edges to rest on the rollers, the guiding effect is lost when the sheet metal becomes sufficiently separated from the wood. In recognition of the fact that such malfunctioning of the pallets can take place, it is common to make gravity-flow rack systems relatively short, which limits the amount of goods that can be stored in one group of racks and makes it necessary to handle the pallets by a fork lift or handjack device relatively frequently.